1. Field of the Invention
The field of the invention is data processing, or, more specifically, methods, apparatus, and products for off-die termination of memory module signal lines in a computer memory subsystem.
2. Description of Related Art
The development of the EDVAC computer system of 1948 is often cited as the beginning of the computer era. Since that time, computer systems have evolved into extremely complicated devices. Today's computers are much more sophisticated than early systems such as the EDVAC. Computer systems typically include a combination of hardware and software components, application programs, operating systems, processors, buses, memory, input/output devices, and so on. As advances in semiconductor processing and computer architecture push the performance of the computer higher and higher, more sophisticated computer software has evolved to take advantage of the higher performance of the hardware, resulting in computer systems today that are much more powerful than just a few years ago.
Computer systems today have increasingly more powerful processors and increasingly greater memory use. Many computer systems have one or more DIMM sockets in which computer memory in the form of a DIMM is installed. In some computers, a DIMM may be installed but not used. In these cases, on-die termination (‘ODT’) within the memory modules of the DIMM itself is employed to terminate the signal lines of a memory bus in the DIMM socket. If not terminated, the signal lines form stub lines and cause signal reflection.
When a DIMM is not installed in a socket, however, the on-die terminators are removed and there are few options to terminate the signal lines. One way currently employed to terminate such signal lines when a DIMM is not installed in a socket is by using a dummy DIMM that employs ODT but cannot be accessed by a memory controller for typical memory operations—reads, writes, and so on. Dummy DIMMs, however, increase the operational cost of each computer and create a logistical issue, especially in large data centers housing a great number of servers, due to the fact that each dummy DIMM must be physically installed in a socket by a human user.